JP3651201B2 - Control method of intermittent aeration activated sludge process - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for biologically treating sewage, domestic wastewater, and industrial wastewater, and more particularly to a method for controlling a process for removing nitrogen and phosphorus in wastewater.
[0002]
[Prior art]
The treatment of sewage and domestic wastewater is mainly organic matter removal, and biological treatment methods represented by the activated sludge method have been generally used. However, in recent years, eutrophication has become a major problem in closed waters such as lakes, and removal of nitrogen and phosphorus that cause this has become important. Therefore, a treatment method that can remove nitrogen and phosphorus in addition to organic substances has been developed as an improvement method of the activated sludge method. Typical methods include A ₂ O method, batch activated sludge method, and intermittent aeration activated sludge method. Etc. These methods are collectively referred to as an anaerobic aerobic activated sludge method because organic substances, nitrogen, and phosphorus are removed by alternating microorganisms in an aerobic condition and an anaerobic condition.
[0003]
Here, the principle of sewage treatment for the purpose of removing nitrogen and phosphorus will be briefly described. The organic matter in the sewage becomes the food of microorganisms constituting the activated sludge and is decomposed and removed. Nitrogen is oxidized under the aerobic condition by NH ₄ -N (ammonia nitrogen) to NO ₃ -N (nitrate nitrogen) by the action of nitrifying bacteria, and then NO by the action of denitrifying bacteria under anaerobic conditions. _3- N is reduced to N ₂ (nitrogen gas) and removed. The relationship between nitrification and denitrification can be summarized as follows.
Reaction Nitrogen form Reaction conditions Microbial nitrification reaction Ammonia nitrogen → Nitrate nitrogen Aerobic (with dissolved oxygen) Nitrification denitrification reaction Nitrate nitrogen → Nitrogen gas Anaerobic (no dissolved oxygen) Denitrifying bacteria By alternately changing the operating conditions between aerobic and anaerobic, activated sludge having the property of accumulating a large amount of phosphorus in the cells is created in the reaction tank and removed using this activated sludge. In other words, this activated sludge releases phosphorus stored in the body to store organic substances in water under anaerobic conditions, and uses organic substances stored in the body under aerobic conditions. It has the property of absorbing phosphorus in water. Dephosphorization is performed by removing activated sludge that has absorbed a large amount of phosphorus from the treatment system as excess sludge.
This relationship can be organized as follows.
Phosphorus concentration in reaction vessel Organic reaction conditions Phosphorus removal Phosphorus release Increase Storage Anaerobic (no dissolved oxygen) −
Phosphorus absorption Reduction Consumption Aerobic (with dissolved oxygen) Extraction of activated sludge As described above, two conditions of aerobic and anaerobic are indispensable for removing nitrogen and phosphorus, but strictly speaking, anaerobic conditions for denitrification Unlike the anaerobic conditions for dephosphorization, the release of phosphorus from the activated sludge occurs after oxygen molecules due to NO ₃ -N disappear in the reaction tank after denitrification, and this is the next aeration This leads to absorption of phosphorus in the process.
[0004]
Next, the anaerobic and aerobic activated sludge method in a typical batch apparatus for small-scale sewage treatment will be described.
The activated sludge method using a batch apparatus is said to be a batch activated sludge process, and the method for removing nitrogen and phosphorus in the apparatus is described in Japanese Patent Application Laid-Open No. 7-136683 filed by the present inventors. Can be summarized as follows:
[0005]
FIG. 6 is a schematic diagram showing the main configuration of the apparatus used in the batch activated sludge method. In FIG. 6, the water and air paths are represented by solid arrows and the control signals are represented by dotted arrows along with the apparatus configuration. is there. In FIG. 6, this apparatus is mainly composed of a reaction tank 2 in which sewage 1 flows in and processing is performed, and a treated water discharge device 4 that discharges treated water 3. The control system comprises a DO meter 5 that measures the dissolved oxygen concentration, a control device 9 that outputs a control signal to the DO control inverter 6, the aeration blower 7, and the aeration stirring device 8 based on the DO measurement value and the control sequence. Yes.
[0006]
A typical operation method in this apparatus is a process cycle (hereinafter sometimes simply referred to as a cycle) consisting of a combined stirring / aeration process, an activated sludge settling process, and a treated water discharge process for 6 hours. In the reaction tank 2, stirring and aeration are intermittently repeated several times within 4 hours after the start of the cycle (intermittent aeration treatment step), and then the precipitation is performed for 1 hour and the treated water is discharged for 1 hour. During the intermittent aeration process in this cycle, the reactions of nitrification, denitrification, phosphorus release and phosphorus absorption proceed, and nitrogen and phosphorus are removed. In such operation, DO is controlled to about 2 mg / L depending on water quality and operating conditions, and when the DO set value is appropriate, removal of nitrogen and phosphorus is good.
[0007]
Moreover, the apparatus which used the two aeration tanks of the 1st aeration tank in which waste_water | drain flows in, and the 2nd aeration tank connected in series with this 1st aeration tank, and provided the final sedimentation tank after that, and its control method are this. This is described in JP-A-6-55190 filed by the inventors.
FIG. 7 is a schematic diagram showing a configuration of a main part of an apparatus for explaining the intermittent aeration method and control system described in JP-A-6-55190. The outline of the apparatus will be described below with reference to FIG. In FIG. 7, the path of water and air is represented by solid arrows, and the control signal system is represented by dotted arrows, and this apparatus is mainly a first in which sewage 1 flows and organic matter, nitrogen and phosphorus are removed by activated sludge. It comprises an aeration tank 2a and a second aeration tank 2b, a final sedimentation basin 4 in which activated sludge is separated by gravity sedimentation to obtain treated water 3, and a return sludge pump 5 that returns the settled activated sludge to the first aeration tank 2a. Yes. The volume ratio of the first aeration tank 2a and the second aeration tank 2b is approximately 1: 1, and the total residence time of the treated water is 16 to 32 hours. The control system includes an ORP meter 6a that measures the oxidation-reduction potential in the first aeration tank 2a, an ORP meter 6b that measures the oxidation-reduction potential in the second aeration tank 2b, and the first aeration blower 7a, the first 2 It consists of the control apparatus 9 which outputs the control signal to the aeration blower 7b, the 1st stirring pump 8a, and the 2nd stirring pump 8b.
[0008]
A typical control method in this apparatus is to set the aeration time to 1 hour, set the DO of the first aeration tank 2a at the aeration time to 0.2 mg / L, perform DO control, and set the agitation time for the first agitation time. 2 Measure the rate of change of the ORP in the aeration tank 2b, detect the ORP inflection point by calculation, stop stirring immediately after detection and open the aeration, and the first aeration tank 2a and the second aeration tank The aeration and stirring of 2b are linked.
[0009]
In the treatment process, low DO control is performed in the first aeration tank 2a, and nitrification and denitrification proceed simultaneously (aerobic denitrification), and the second aeration tank 2b actively nitrifies with DO of about 2 to 3 mg / L. At the same time, and absorbs phosphorus into activated sludge. And after 1 hour progress, it transfers to a stirring process automatically. In the agitation process, since aerobic denitrification has progressed in the first aeration tank 2a in the previous aeration process, NO ₃ -N has a low concentration, and denitrification is completed in a short time. Phosphorus is released. Moreover, since the organic substance concentration is low in the second aeration tank 2b, denitrification proceeds slowly and simultaneously the ORP decreases. Since the ORP has a reaching point when denitrification is completed, the bending point is detected, stirring is stopped, and aeration is performed. Therefore, release of phosphorus hardly occurs in the second aeration tank 2b. That is, in the stirring step, phosphorus is mainly released in the first aeration tank 2a and denitrification is performed in the second aeration tank 2b. Since the above method uses two aeration tanks, it has a feature that raw water is discharged without treatment as compared with the case where there is one aeration tank.
[0010]
[Problems to be solved by the invention]
The control method between the batch activated sludge method and the intermittent aeration activated sludge method in the case of an apparatus in which two reaction tanks are connected in series has been described above. However, phosphorus removal is poor due to changes in water quality and operating conditions. May be. Despite the fact that there are enough dephosphorizing bacteria that accumulate a large amount of phosphorus in the cell and biological phosphorus is absorbed and released, phosphorus removal may be insufficient. For some reason, dephosphorization stores less organic matter for phosphorus absorption, and biological phosphorus release and absorption occurs, but the amount of released phosphorus is the same as the amount of absorbed phosphorus, or There is a problem that the amount of phosphorus to be absorbed is reduced, and phosphorus in the treated water cannot be completely absorbed.
[0011]
This invention is made | formed in view of the above-mentioned problem, The objective provides the control method of the intermittent aeration type activated sludge process which recovers the removal of phosphorus satisfactorily when the removal of phosphorus becomes poor. That is.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the control method of the present invention is performed as follows.
1st invention uses the batch type apparatus which processes waste water by repeating the processing cycle which consists of the stirring / aeration combined process, the activated sludge precipitation process, and the treated water discharge process in the reaction tank into which the waste water flows. In the control method of the intermittent aeration activated sludge method that removes nitrogen and phosphorus in the wastewater, a pH meter is installed, and the pH value in the stirring process is made lower than the pH in the reaction tank at the start of the stirring process; To do.
[0013]
In the control method according to the first aspect of the present invention, phosphorus is released when nitric acid is exhausted in the tank in the stirring step set for a predetermined time (for example, 1 hour). In general, if the pH is constant, the amount of phosphorus released is proportional to the amount of organic matter stored in the body by the dephosphorizing bacteria. However, if the amount of organic matter in the reaction tank is constant, the pH is usually as shown in FIG. When it is higher, more energy is required for the organic matter to pass through the cell membrane of the microorganism than usual, and the amount of phosphorus released per unit time increases, and the release rate of phosphorus increases. At this time, there is little organic matter accumulated in the body, and the organic matter intake rate is slow. Conversely, when the pH is lower than normal, less energy is required for the organic substance to pass through the cell membrane of the microorganism, and the amount of phosphorus released per unit time is small, and the phosphorus release rate is slow. At this time, many organic substances are accumulated in the body, and the organic substance intake speed is increased. Therefore, in the stirring process, the intake efficiency of organic substances can be increased by controlling the pH in the reaction tank to be low. As a result, the lower the pH, the more organic matter is stored, the amount of phosphorus released to store the same organic matter can be reduced, and the amount of phosphorus that can be absorbed is increased in proportion to the amount of organic matter stored by the microorganism. The amount of phosphorus that must be absorbed during the aeration process can be reduced.
[0014]
In the second invention, waste water is allowed to flow into an aeration tank, and an aerobic state in which aeration is performed and an anaerobic state in which aeration is stopped and agitation is repeated alternately. In the control method of the intermittent aeration activated sludge method in which the precipitated sludge is returned to the aeration tank and is extracted as excess sludge and nitrogen and phosphorus in the drainage are removed, the first aeration tank into which the wastewater flows and the first aeration tank. In a device that performs processing using a second aeration tank connected in series to one aeration tank, a pH meter is installed in the first aeration tank, and the pH value in the stirring process is determined from the pH in the reaction tank at the start of the stirring process. Will be lowered.
[0015]
The control method of the second invention is the same as that of the first invention. In the stirring step of the first aeration tank, that is, the phosphorus release process, the pH in the reaction tank is controlled to be lower than usual to increase the accumulated amount of organic matter. Thus, when phosphorus removal is poor, reducing the amount of phosphorus released and reducing the amount of phosphorus that must be absorbed, the phosphorus absorption in the second aeration tank can be performed smoothly.
[0016]
According to the above method, since an appropriate phosphorus release amount and phosphorus absorption amount are ensured, phosphorus removal can be improved when phosphorus removal is poor.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the intermittent aeration activated sludge method according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the main configuration of a batch type apparatus and control system of an intermittent aeration activated sludge method to which the present invention is applied. 1, this apparatus is basically the same as the apparatus shown in FIG. 6 except that an acid addition pump 11, an acid storage tank 12, an alkali addition pump 13, and an alkali storage tank 14 are installed. is there.
[0018]
FIG. 2 shows changes in phosphorus and pH when the control method of the first invention is used. FIG. 2 (a) shows the phosphorus concentration PO ₄ -P, and FIG. 2 (b) shows the pH time characteristics. Basically, one cycle consists of a total of 6 hours including 1 hour of stirring, 1 hour of aeration, 1 hour of stirring, 1 hour of aeration, 1 hour of precipitation, and 1 hour of discharge. At the start of the cycle, sewage is introduced at the same time as the stirring step is started, and after denitrification is completed, PO ₄ -P is released. When the stirring step is completed, an aeration step is started and PO ₄ -P absorption begins. At the start of the stirring process, acid is added from the acid storage tank 12 to the reaction tank using the acid addition pump 11 so that the pH in the reaction tank is about 0.5 lower than the pH value at the start of the stirring process. The pH in the reaction vessel is lowered. By lowering the pH, the energy of the organic substance passing through the cell membrane can be reduced, and the intake rate of the organic substance can be increased. Therefore, many organic substances can be stored with a small amount of released phosphorus. When the pH is low and the amount of released phosphorus is the same, the lower the pH, the more organic matter is stored by the microorganism. In proportion to the amount of stored organic matter, it is believed that the amount of phosphorus absorbed is also proportional to it. When the stirring step is completed, alkali is added from the alkali storage tank 14 to the reaction tank using the alkali addition pump 13 so that the pH in the reaction tank is lowered to the original value, and the pH in the reaction tank is determined. Return to. After repeating this stirring and aeration process twice, it moves to the precipitation process which isolate | separates activated sludge and treated water, and discharges | emits supernatant water after that. In addition, agitation and aeration during one cycle can be applied to each control method.
[0019]
FIG. 3 is a schematic diagram showing the main configuration of an apparatus and a control system using the first and second aeration tanks of the intermittent aeration activated sludge method to which the present invention is applied. 3, this apparatus is basically the same as the apparatus shown in FIG. 7, except that an acid addition pump 11, an acid storage tank 12, an alkali addition pump 13, and an alkali storage tank 14 are installed. .
[0020]
FIG. 4 shows changes in phosphorus and pH when the control method of the second invention is used.
4A shows the phosphorus concentration PO ₄ -P in the first aeration tank, FIG. 4B shows the pH of the first aeration tank, and FIG. 4C shows the phosphorus concentration PO ₄ in the second aeration tank. The time course characteristics of the pH of the second aeration tank are shown in FIG. Basically, one cycle consists of 2 hours. The first aeration tank comprises 30 minutes of aeration, 1 hour and 30 minutes of stirring, and the second aeration tank comprises 1 hour of aeration and 1 hour of stirring. The inflow of sewage is intermittently performed in the first aeration tank. In the first aeration tank, the aeration process starts at the start of the cycle, and phosphorus absorption and nitrification begin. After 30 minutes, it moves to an aeration process and denitrification is performed. During this time, no release of phosphorus occurs because nitrate nitrogen remains in the reaction vessel. Phosphorus release occurs after denitrification. After detecting the bending point from the output of the ORP meter, the acid storage tank 12 is used to react the reaction tank from the acid storage tank 12 so that the pH in the reaction tank is about 0.5 lower than the pH value at the start of the stirring process. The acid in the reactor is added to lower the pH in the reaction vessel. By reducing the pH, it becomes possible to increase the amount of organic matter stored by the dephosphorizing bacteria. In the second aeration tank, an aeration process for phosphorus absorption and nitrification starts at the start of the cycle, and is performed for about 1 hour until the ORP inflection point of the first aeration tank is detected. During this time, the phosphorus concentration of sewage flowing from the first aeration tank into the second aeration tank is low, and the phosphorus concentration in the second aeration tank is almost zero. After detecting the ORP inflection point of the first aeration tank, the process proceeds to the stirring step. In the stirring process, denitrification is performed, and the stirring process is performed until the ORP inflection point of the second aeration tank is detected. After the ORP inflection point of the second aeration tank is detected, the cycle is returned to both the first aeration tank and the second aeration tank. At this time, alkali is added from the alkali storage tank 13 to the reaction tank using the alkali addition pump 13 so that the pH in the reaction tank lowered in the first aeration tank becomes the original value, and the pH in the reaction tank is increased. Return to the original.
[0021]
The release of phosphorus is related to the reaction in which microorganisms store organic substances in cells, and the release rate of phosphorus is affected by the pH in the reaction tank. FIG. 5 shows changes in phosphorus concentration when the pH is changed. When the pH is higher than usual, a large amount of energy is required for the organic substance to pass through the cell membrane, the amount of phosphorus released increases, and the amount of stored organic substance decreases. Further, when the pH is lower than usual, less energy is required for the organic substance to pass through the cell membrane, the amount of released phosphorus is small, and the amount of stored organic substance is large. In general, the amount of phosphorus released is related to pH and the amount of stored organic matter, and the amount of phosphorus absorbed is related to the amount of stored organic matter. If the pH is the same, the greater the amount of phosphorus released, the greater the amount of stored organic matter. If the amount of released phosphorus is the same, the lower the pH, the greater the amount of stored organic matter. The amount of phosphorus absorbed is hardly affected by pH, and when the amount of organic matter stored by the microorganism is large, the amount of absorption is also large. Since the pH of the sewage is around 7.0, by controlling the pH to about 6.5 in the stirring process, reducing the amount of phosphorus released and increasing the storage amount of organic matter, it is possible to achieve an appropriate phosphorus in the stirring time. The release amount can be secured, the amount of phosphorus absorbed in the subsequent aeration process can be increased, and the phosphorus removal can be recovered when the phosphorus removal is defective.
[0022]
【The invention's effect】
In the control method of the conventional intermittent aeration activated sludge method, there has been a problem that the phosphorus removal rate of the treated water is poor even though phosphorus is released and absorbed.
The control method of the present invention made to cope with this has the following advantages. That is, the control method of the first invention is a batch process in which wastewater is treated by repeating a treatment cycle comprising a stirring / aeration combined process, an activated sludge precipitation process, and a treated water discharge process in a reaction tank into which the wastewater flows. In the control method of the intermittent aeration activated sludge method that removes nitrogen and phosphorus in the wastewater using a type device, a pH meter is installed, and the pH value in the stirring process is determined from the pH in the reaction tank at the start of the stirring process. By lowering the amount, the organic substance can be stored with a small amount of released phosphorus, and the load of phosphorus in the aeration process can be reduced.
[0023]
The control method according to the second aspect of the present invention is a method in which wastewater is allowed to flow into an aeration tank, and an aerobic state in which aeration is performed and an anaerobic state in which aeration is stopped and agitated are alternately repeated, and then this process is performed. In the control method of the intermittent aeration activated sludge method in which water is discharged from the final sedimentation basin, the precipitated sludge is returned to the aeration tank, and is extracted as surplus sludge to remove nitrogen and phosphorus in the wastewater, the first inflow of wastewater. In an apparatus that performs processing using an aeration tank and a second aeration tank connected in series to the first aeration tank, a pH meter is installed in the first aeration tank, and the pH value in the agitation process is a reaction at the start of the agitation process. By making it lower than the pH in the tank, appropriate phosphorus release can be performed in the first aeration tank, and phosphorus absorption in the second aeration tank can be reliably performed.
[0024]
As described above, when phosphorus removal becomes poor by the normal operation control method, the amount of absorption can be increased more than the amount of phosphorus released by using the control method of the present invention, and the phosphorus removal of treated water is improved. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a main configuration of an apparatus to which a control method of a first invention is applied.
FIGS. 2A and 2B show changes in water quality and pH in a reaction tank of an apparatus to which the control method of the first invention is applied, wherein FIG. 2A is a relationship line of PO ₄ -P, and FIG. Figure.
FIG. 3 is a schematic diagram showing the main configuration of an apparatus to which the control method of the second invention is applied.
FIG. 4 shows changes in water quality and pH in a reaction tank of an apparatus to which the control method of the second invention is applied, (a) shows the phosphorus concentration PO ₄ -P in the first aeration tank, and (b) shows the first. (C) is the relationship between the pH of the aeration tank, the phosphorus concentration PO ₄ -P of the second aeration tank, and (d) the pH of the second aeration tank with respect to time.
FIG. 5 is a relationship diagram showing a change in phosphorus release amount due to a difference in pH.
FIG. 6 is a schematic diagram showing a main configuration of an apparatus to which a conventional control method is applied.
FIG. 7 is a schematic diagram showing a main configuration of an apparatus to which a conventional control method is applied.
[Explanation of symbols]
1: Sewage 2: Reaction tank 2a: First aeration tank 2b: Second aeration tank 3: Treated water 4: Treated water discharge device 4a: Final sedimentation tank 5: DO meter 5a: Return sludge pump 6: Inverter 6a: First ORP meter 6b: second ORP meter 7: aeration blower 7a: first aeration blower 7b: second aeration blower 8: aeration agitating device 8a: first agitation pump 8b: second agitation pump 9: control device 10: pH Total 11: Acid addition pump 12: Acid storage tank 13: Alkali addition pump 14: Alkaline storage tank

Claims (2)

In the reaction tank into which the wastewater flows, nitrogen in the wastewater is collected using a batch system that treats the wastewater by repeating the treatment cycle consisting of the combined stirring / aeration process, the activated sludge precipitation process, and the treated water discharge process. In the control method of the intermittent aeration activated sludge process for removing phosphorus, a pH meter is installed, and the intermittent aeration type is characterized in that the pH value in the stirring process is lower than the pH in the reaction tank at the start of the stirring process Control method of activated sludge process. The wastewater is allowed to flow into the aeration tank, and after treatment, the aerobic state in which aeration is performed and the anaerobic state in which aeration is stopped and agitation is repeated alternately, the treated water is discharged from the final sedimentation basin, and the precipitated sludge Is returned to the aeration tank, and in the intermittent aeration activated sludge control method that removes excess sludge and removes nitrogen and phosphorus in the wastewater, the first aeration tank into which the wastewater flows and the first aeration tank in series In the apparatus that performs processing using the connected second aeration tank, a pH meter is installed in the first aeration tank, and the pH value in the stirring process is made lower than the pH in the reaction tank at the start of the stirring process. Control method of intermittent aeration activated sludge process.

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